• Learn about your local tap water by getting an annual water-quality report from the supplier.

• Test your household water for lead, which most commonly comes from pipes in older homes.

• Consider using a filter, especially if you uncover concerns. Inexpensive pitchers and faucet attachments using carbon filters reduce lead and some other substances. But always read the labels and check for certification from NSF International. And change the filters as often as the manufacturer recommends.

• Take extra precautions if you have impaired immunity as a result of chemotherapy, HIV or other health problems. Filters that rely on "reverse osmosis" or "absolute one micron filters" can remove dangerous parasites. Bottled waters treated with those methods or with distillation or ultraviolet light also can be good choices — but read the label or check with the bottler to confirm the treatment method.

As the final long, hot weekend of summer approaches, many of us will reach for a few cold ones — drinks of water, that is.

But should that water come from a tap or a bottle? And does the choice make any difference from a health standpoint?

Those questions are timely after a summer in which bottled water took a few hard knocks. First, the U.S. Conference of Mayors called for a study of the environmental effect of all those plastic bottles, most of which are not recycled. San Francisco banned city employees from spending tax dollars on bottled water. And Pepsico changed the label on its Aquafina bottles to more clearly reflect the fact that the stuff inside is filtered tap water (as are several other popular brands, including Dasani, from Coca-Cola).

One reason that change raised eyebrows is that tap water has its own image problems. This summer, the spotlight was on Washington, D.C., where a watchdog group found elevated levels of toxic chlorination byproducts in the drinking water — levels that local officials said were probably temporary.

But "we could have done that study in any city and might have found the same thing," says Jane Houlihan, vice president for research at the Environmental Working Group, which conducted the study. (For details, visit www.ewg.org).

What's a consumer to do?

Before you reach for a soda, rest assured: Water remains the ultimate health drink — free of calories, sweeteners or caffeine, perfectly suited to hydrate the human body and, in the USA, almost always safe, whatever its source.

"The United States continues to have some of the best drinking water standards in the world," says Jon Coifman, spokesman for the Natural Resources Defense Council. The non-profit group has studied the safety of both bottled and tap water. (For information, visit www.nrdc.org/water/drinking/brief.asp).

Bottled water, which is regulated by the Food and Drug Administration, "is not tested as thoroughly or as frequently" as tap water, which is regulated by the Environmental Protection Agency, Coifman says. "It's not that bottled water is going to kill you. … But there's also no reason to believe it's better," despite marketing that is all about "health, wholesomeness and purity."

Houlihan concurs: "People may be turning to bottled water because they don't trust their tap water. … But you don't have any assurance of better safety."

Water bottlers, for their part, say they don't claim their products are safer.

"It's unfortunate that people are turning this into a tap-water-vs.-bottled-water issue," says Joseph Doss, president of the International Bottled Water Association. "We don't disparage tap water. We think if consumers are drinking water, whether it's bottled or tap, it's a good thing."

The association ran ads this summer defending bottled water as healthful in a country where people are battling obesity, diabetes and heart disease and where "70% of all beverages consumed are from a container."

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